Communication method and communication apparatus

ABSTRACT

A communication method of the present disclosure comprises transmitting a sounding frame comprising a training signal; and receiving a first feedback frame from a communication partner device, the first feedback frame comprising first beamforming feedback information, wherein the first feedback frame is transmitted together with at least one second feedback frame by multiuser transmission.

BACKGROUND 1. Technical Field

The present disclosure generally pertains to communication networks and,more particularly, to sounding method in wireless local area networksbased on OFDMA (Orthogonal Frequency Division Multiple Access) andMU-MIMO (Multi-User Multiple Input Multiple Output).

2. Description of the Related Art

The IEEE (Institute of Electrical and Electronics Engineers) 802.11Working Group is developing 802.11ax HE (High Efficiency) WLAN (WirelessLocal Area Network) air interface in order to achieve a very substantialincrease in the real-world throughput achieved by users in high densityscenarios while keeping backward compatibility with legacy802.11a/g/n/ac standards. MU-MIMO (Multi-User Multiple Input MultipleOutput) and OFDMA (Orthogonal Frequency Division Multiple Access)transmission have been envisioned as two of the most important featuresin 802.11ax See, for example, IEEE Std 802.11ac-2013 and IEEE Std802.11n-2009.

SUMMARY

Studies are underway to perform efficient sounding for UL (Up Link) MU(Multi-User) communications in 802.11ax, e.g., UL OFDMA communicationsor UL MU-MIMO communications.

In one general aspect, the techniques disclosed here feature acommunication method comprising transmitting a sounding frame comprisinga training signal and receiving a first feedback frame from acommunication partner device, the first feedback frame comprising firstbeamforming feedback information, wherein the first feedback frame istransmitted together with at least one second feedback frame bymultiuser transmission.

With the present disclosure, it is possible to achieve efficientsounding for UL MU transmission.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram illustrating an example WLAN;

FIG. 2 shows a diagram illustrating an example PPDU according to theprior art;

FIG. 3 shows a schematic timing diagram illustrating an example soundingprocedure and an example UL MU-MIMO transmission based on the examplesounding procedure, according to the prior art;

FIG. 4 shows a schematic timing diagram illustrating an example soundingprocedure and an example UL MU transmission based on the examplesounding procedure, according to a first embodiment of the presentdisclosure;

FIG. 5 shows a diagram illustrating an example feedback frame accordingto the first embodiment of the present disclosure;

FIG. 6 shows a schematic timing diagram illustrating an example soundingprocedure and an example UL MU transmission based on the examplesounding procedure, according to a second embodiment of the presentdisclosure;

FIG. 7 shows a schematic timing diagram illustrating an example soundingprocedure and an example UL MU transmission based on the examplesounding procedure, according to a third embodiment of the presentdisclosure;

FIG. 8 shows a schematic timing diagram illustrating an example soundingprocedure and an example UL MU transmission based on the examplesounding procedure, according to a fourth embodiment of the presentdisclosure;

FIG. 9 shows a schematic timing diagram illustrating an example soundingprocedure and an example UL MU transmission based on the examplesounding procedure, according to a fifth embodiment of the presentdisclosure;

FIG. 10 shows a schematic timing diagram illustrating an examplesounding procedure and an example UL MU transmission based on theexample sounding procedure, according to a sixth embodiment of thepresent disclosure;

FIG. 11 shows a flow chart illustrating a first example method,implemented by AP, for performing sounding with STAs for UL MUtransmission according to the present disclosure;

FIG. 12 shows a flow chart illustrating a first example method,implemented by STA, for performing sounding with AP for UL MUtransmission according to the present disclosure;

FIG. 13 shows a flow chart illustrating a second example method,implemented by AP, for performing sounding with STAs for cascaded DL andUL MU transmission according to the present disclosure;

FIG. 14 shows a flow chart illustrating a second example method,implemented by STA, for performing sounding with AP for cascaded DL anUL MU transmission according to the present disclosure;

FIG. 15 shows a block diagram illustrating an example configuration ofAP according to the present disclosure; and

FIG. 16 shows a block diagram illustrating an example configuration ofSTA according to the present disclosure.

DETAILED DESCRIPTION

Various embodiments of the present disclosure will now be described indetail with reference to the annexed drawings. In the followingdescription, a detailed description of known functions andconfigurations has been omitted for clarity and conciseness.

<Underlying Knowledge Forming Basis of the Present Disclosure>

FIG. 1 is a diagram of an example WLAN (Wireless Local Area Network)100. The WLAN 100 comprises an AP (Access Point) 102 and a plurality ofSTAs (Stations) 104 that are associated with the AP 102. In the downlink(DL) of the WLAN 100, the AP 102 may be configured to transmitrespective data stream to multiple STAs 104 simultaneously via DL MUcommunications (i.e., DL MU-MIMO or DL OFDMA communications). Similarly,in the uplink (UL) of the WLAN 100, multiple STAs 104 can transmitrespective data streams to the AP 102 simultaneously via UL MUcommunications (i.e., UL MU-MIMO or UL OFDMA communications).

As for DL or UL OFDMA communications, data streams are transmittedsimultaneously to or by a group of STAs over respective subbands, eachof which comprises a plurality of subcarriers. A data stream may betransmitted to or by a single STA over a specific subband using SU-MIMO(Single User MIMO) technique. Alternatively, data streams may betransmitted simultaneously to or by multiple STAs over a specificsubband using MU-MIMO technique.

As for DL or UL MU-MIMO communications, data streams are transmittedsimultaneously to or by a group of STAs over the entire bandwidth usingMU-MIMO technique.

In SU-MIMO technique, transmit beamforming matrices may be used toprecode data for a particular STA such that the link throughput ismaximized at the receiver output of the particular STA. In MU-MIMOtechnique, respective transmit beamforming matrices may be used toprecode respective data streams for each STA in a group of STAs, suchthat the total throughput (e.g., the sum performance or max-minfairness) is maximized. For a particular STA, transmit beamformingmatrices used for MU-MIMO transmission are generally different fromtheir counterparts for SU-MIMO transmission since the former needs totake into account multiuser interference that exists in MU-MIMOtransmission. In summary, prior to any DL or UL MU transmission, the AP102 needs to interact with the STAs 104 via a sounding procedure to makenecessary preparations, such as user grouping, subband allocation, anddevelopment of transmit beamforming matrices, etc.

FIG. 2 is a diagram of an example Physical Layer Protocol Data Unit(PPDU) 200 according to the prior art [see IEEE 802.11-15/0132r7,Specification Framework for TGax, July 2015 and IEEE 802.11-15/0579r3,802.11ax Preamble Design and Auto-detection, July 2015]. The PPDU 200 isan OFDMA PPDU which includes four OFDM data units 202-1, 202-2, 202-3and 202-4 in an 80 MHz channel bandwidth. In context of DL MUtransmission, the PPDU 200 is generated by the AP 102 in FIG. 1, suchthat the OFDM data unit 202-1 is transmitted to the STA 104-1 over afirst 10 MHz subband, the OFDM data unit 202-2 is transmitted to the STA104-2 over a second 10 MHz subband, the OFDM data unit 202-3 istransmitted to the STA 104-3 over a 20 MHz subband and the OFDM dataunit 202-4 is transmitted to the STAs 104-4 and 104-5 over a 40 MHzsubband. In context of UL MU transmission, on the other hand, the PPDU200 is generated by the STAs 104 collectively such that the OFDM dataunit 202-1 is transmitted by the STA 104-1 to the AP 102 over a first 10MHz subband, the OFDM data unit 202-2 is transmitted by the STA 104-2 tothe AP 102 over a second 10 MHz subband, the OFDM data unit 202-3 istransmitted by the STA 104-3 to the AP 102 over a 20 MHz subband and theOFDM data unit 202-4 is transmitted by the STAs 104-4 and 104-5 to theAP 102 over a 40 MHz subband.

It should be noted that if a PPDU only includes a single OFDM data unitwhich is transmitted by or to the AP 102 over the entire bandwidth usingMU-MIMO technique, the PPDU becomes a DL or UL MU-MIMO PPDU. If a PPDUonly includes a single OFDM data unit which is transmitted by or to theAP 102 over the entire bandwidth using a technique other than MU-MIMO,the PPDU becomes a DL or UL SU PPDU.

As illustrated in FIG. 2, the PPDU 200 comprises a legacy short trainingfield (L-STF) 204, a legacy long training field (L-LTF) 206, a legacysignal field (L-SIG) 208, a repeated legacy signal field (RL-SIG) 210, afirst high efficiency signal field (HE-SIG-A) 212, a second highefficiency signal field (HE-SIG-B) 214, a high efficiency short trainingfield (HE-STF) 216, a high efficiency long training field (HE-LTF) 218and a high efficiency data portion (HE Data) 220. The L-STF 204, L-LTF206 and L-SIG 208 facilitate backward compatibility with legacy802.11a/g/n/ac standards. The RL-SIG 210 is used for auto-detection ofthe frame format of the PPDU 200. Each of the HE-SIG-A 212 and theHE-SIG-B 214 carries control information required to interpret the PPDU200, e.g., channel bandwidth. In particular, the HE-SIG-B 214 containscontrol information for designated receiving STAs especially for DL MUtransmission. The HE-SIG-B 214 is partitioned into two portions:HE-SIG-B1 and HE-SIG-B2, which carry different control signaling. TheHE-SIG-B 214 does not exist in the PPDU 200 if it is an UL MU PPDU, DLSU PPDU or UL SU PPDU. The HE-STF 216 is used to train AGC (AutomaticGain Control) for receiving the HE Data portion 220 of a correspondingOFDM data unit 202. The HE-LTF 218 comprises a plurality of HE-LTFsymbols and is used to generate MIMO channel estimate for receiving andequalizing the HE Data portion 220 of the corresponding OFDM data unit202.

The L-STF 204, L-LTF 206, L-SIG 208, RL-SIG 210, HE-SIG-A 212 andHE-SIG-B 214 occupy a smallest bandwidth supported by the WLAN 100(e.g., 20 MHz). If the PPDU 200 occupies a bandwidth that is greaterthan the smallest bandwidth of the WLAN 100, then the L-STF 204, L-LTF206, L-SIG 208, RL-SIG 210 and HE-SIG-A 212 may be duplicated and mappedin each smallest bandwidth portion of the PPDU 200 (e.g., in each 20 MHzportion of the PPDU 200). The HE-SIG-B1 and HE-SIG-B2 of HE-SIG-B 214may alternatively be duplicated and mapped in each smallest bandwidthportion of the PPDU 200.

On the other hand, the HE-STF 216, the HE-LTF 218 and the HE Dataportion 220 occupy an entire bandwidth of the corresponding OFDM dataunit 202. For example, the OFDM data unit 202-4 occupies 40 MHz, whereinthe HE-STF 216, HE-LTF 218 and HE data portion 220 occupy the entire 40MHz bandwidth of the OFDM data unit 202-4.

FIG. 3 is a schematic timing diagram illustrating an example soundingprocedure 300 and an example UL MU-MIMO transmission based on thesounding procedure 300, according to the prior art (see U.S. PatentApplication No. 2015/0146812A1). The sounding procedure 300 is anexplicit sounding procedure in which the AP 102 derives a channelestimate corresponding to a communication channel from a STA to the AP102 directly from a sounding frame transmitted by the STA to the AP 102.

During a time interval 322-1, the AP 102 transmits a soundingannouncement frame 302-1 to the STA 104-1 to request the STA 104-1 totransmit a sounding frame. During a time interval 324-1, in response toreceiving the sounding announcement frame 302-1, the STA 104-1 sends asounding frame 304-1 to the AP 102. The AP 102 obtains, based ontraining signals included in the sounding frame 304-1, a channelestimate characterizing the communication channel from the STA 104-1 tothe AP 102. Furthermore, based on the channel estimate characterizingthe communication channel from the STA 104-1 to the AP 102, the AP 102generates beamforming feedback information for the STA 104-1. During atime interval 326-1, the AP 102 transmits a feedback frame 306-1 to theSTA 104-1 that includes the beamforming feedback information for the STA104-1. The STA 104-1 uses the received beamforming feedback frame 306-1to generate its transmit beamforming matrices for UL MU-MIMOtransmission.

The AP 102 may sequentially prompt other STAs (e.g., 104-2 and 104-3) totransmit sounding frames, obtain a channel estimate characterizing thecommunication channel from each of other STAs to the AP 102, andtransmit beamforming feedback to each of other STAs. For example, duringa time interval 322-2, the AP 102 sends a sounding announcement frame302-2 to the STA 104-2. During a time interval 324-2, in response toreceiving the sounding announcement frame 302-2, the STA 104-2 sends asounding frame 304-2 to the AP 102. The AP 102 obtains, based ontraining signals included in the sounding frame 304-2, a channelestimate characterizing the communication channel from the STA 104-2 tothe AP 102 and further generates beamforming feedback information forthe STA 104-2. During a time interval 326-2, the AP 102 transmits afeedback frame 306-2 to the STA 104-2, which includes the beamformingfeedback information for the STA 104-2. The STA 104-2 uses the receivedbeamforming feedback frame 306-2 to generate its transmit beamformingmatrices for UL MU-MIMO transmission. The same sounding procedure isperformed between the AP 102 and the STA 104-3 in the following timeintervals 322-3, 324-3 and 326-3.

During a time interval 328 in FIG. 3, based on the received soundingframes 304 (e.g., 304-1, 304-2 and 304-3) from the STAs 104, the AP 102selects a subset of STAs for inclusion into an UL group for UL MU-MIMOtransmission (e.g., the STAs 104-1 and 104-2 in this example). During atime interval 332, the AP 102 transmits a trigger frame 308 to each ofthe STAs in the UL group (e.g., the STAs 104-1 and 104-2 in thisexample) for UL MU-MIMO transmission. The trigger frame 308 prompts theSTAs in the UL group to simultaneously transmit data streams to the AP102 at a particular time interval. During a time interval 334, the STAsin the UL group (i.e., STAs 104-1 and 104-2 in this example) transmitrespective data stream 310 simultaneously to the AP 102 using respectivetransmit beamforming matrices.

According to the prior art, for UL MU-MIMO transmission, the transmitbeamforming matrices used by a particular STA are obtained based on thechannel estimate for the particular STA, not taking into account channelestimates of other STAs that belong to the same UL group as theparticular STA. Therefore, the transmit beamforming matrices may not beinstrumental for mitigating multiuser interference in UL MU-MIMOtransmission. As a result, even if an advanced receiver is used by theAP 102, it may not be able to suppress multiuser interference in ULMU-MIMO transmission sufficiently and thus the total throughput for ULMU-MIMO transmission may be compromised. In addition, the prior art asillustrated in FIG. 3 cannot handle subband based UL OFDMA transmissionefficiently. The present disclosure is made in light of the foregoingknowledge. The present disclosure is made in light of the foregoingknowledge.

Next, various embodiments for the sounding procedure and thecorresponding UL MU transmission of the present disclosure will beexplained in further details.

First Embodiment

FIG. 4 is a schematic timing diagram illustrating an example soundingprocedure 400 and an example UL MU transmission based on the soundingprocedure 400, according to a first embodiment of the presentdisclosure. The sounding procedure 400 is an explicit sounding procedurein which the AP 102 derives channel state information and/or qualityindicators corresponding to a communication channel from a STA to the AP102, directly from a sounding frame transmitted by the STA to the AP102.

During a time interval 422-1, the AP 102 transmits a soundingannouncement frame 402-1 to the STA 104-1 to initiate the soundingprocedure 400 and to request the STA 104-1 to transmit a sounding frame.During a time interval 424-1, in response to receiving the soundingannouncement frame 402-1, the STA 104-1 sends a sounding frame 404-1 tothe AP 102. The sounding frame 404-1 includes suitable training signalsin the PHY (Physical Layer) preamble (e.g., the HE-LTF field) to allowthe AP 102 to obtain a channel state information and/or qualityindicators of the communication channel from the STA 104-1 to the AP102. The sounding frame 404-1 may also include UL power controlinformation for the STA 104-1 (e.g., transmit power, power adjustablerange and/or power headroom) in the PHY preamble (e.g., HE-SIG-A field).The sounding frame may be a NDP (Null Data Packet) that includes a PHYpreamble only and omits a payload. The AP 102 obtains, based on trainingsignals included in the sounding frame 404-1, channel state information(e.g., gain, phase, SNR (Signal to Noise Ratio), etc.) corresponding tothe entire bandwidth of the communication channel from the STA 104-1 tothe AP 102. Additionally or alternatively, the AP 102 determines qualityindicators (e.g., SNR, SNIR (Signal to Noise plus Interference Ratio),signal strength, etc.) corresponding to one or more subbands of thecommunication channel from the STA 104-1 to the AP 102. Based on qualityindicators corresponding to the one or more subbands of thecommunication channel from the STA 104-1 to the AP 102, the AP 102further identifies one or more candidate subbands for the STA 104-1 tobe used for UL transmission.

The AP 102 may sequentially prompt other STAs (e.g., 104-2 and 104-3) totransmit sounding frames. Based on training signals included in thesounding frames, the AP 102 obtains channel state informationcorresponding to the entire bandwidth of the communication channel fromeach of other STAs to the AP 102 and/or quality indicators correspondingto one or more subbands of the communication channel from each of otherSTAs to the AP 102. Based on the quality indicators corresponding to theone or more subbands of the communication channel from each of otherSTAs to the AP 102, the AP 102 determines one or more candidate subbandsfor each of other STAs to the AP 102. For example, during a timeinterval 422-2, the AP 102 sends a sounding announcement frame 402-2 tothe STA 104-2. During a time interval 424-2, in response to receivingthe sounding announcement frame 402-2, the STA 104-2 sends a soundingframe 404-2 to the AP 102. The AP 102 obtains channel state informationcorresponding to the entire bandwidth of the communication channel fromthe STA 104-2 to the AP 102. Additionally or alternatively, the AP 102determines quality indicators corresponding to one or more subbands ofthe communication channel from the STA 104-2 to the AP 102. The AP 102further identifies one or more candidate subbands for the STA 104-2 tobe used for UL transmission. The same sounding procedure is performedbetween the AP 102 and the STA 104-3 in the following time intervals422-3 and 424-3.

According to the first embodiment of the present disclosure, the AP 102identifies intended usage of transmission scheme for the entirebandwidth and/or each of the one or more candidate subbands for each ofthe STAs based on the channel state information corresponding to theentire bandwidth of the communication channel from each of the STAs tothe AP 102 and/or quality indicators corresponding to the one or morecandidate subbands of the communication channel from each of the STAs tothe AP 102. For example, the AP 102 determines whether the entirebandwidth or each of the one or more candidate subbands for each of theSTAs should be used for UL SU-MIMO transmission, UL MU-MIMO transmissionor both.

According to the first embodiment of the present disclosure, in casethat the AP 102 expects that only a single STA will have buffered datato be transmitted over the entire bandwidth (e.g., only a single STA hasindicated to the AP 102 that it has a large amount of buffered data tobe transmitted), the AP 102 may determine the entire bandwidth should beused only for UL SU-MIMO transmission.

According to the first embodiment of the present disclosure, in casethat the AP 102 expects that two or more STAs will have buffered data tobe transmitted over the entire bandwidth (e.g., the two or more STAshave indicated to the AP 102 that they have a large amount of buffereddata to be transmitted), the AP 102 may determine the entire bandwidthshould be used only for UL MU-MIMO transmission.

According to the first embodiment of the present disclosure, in casethat the AP 102 is uncertain about how the entire bandwidth is used forthe time being, the AP 102 may determine the entire bandwidth should beused for UL SU-MIMO or UL MU-MIMO transmission.

According to the first embodiment of the present disclosure, in casethat a candidate subband is owned by a single STA, the AP 102 maydetermine the candidate subband should be used only for UL SU-MIMOtransmission.

According to the first embodiment of the present disclosure, in casethat a candidate subband is shared by two or more STAs and but the AP102 expects that only one of the two or more STAs will have buffereddata to be transmitted over the candidate subband (e.g., only one of thetwo or more STAs has indicated to the AP 102 that it has buffered datato be transmitted), the AP 102 may determine the candidate subbandshould be used only for UL SU-MIMO transmission.

According to the first embodiment of the present disclosure, in casethat a candidate subband is shared by two or more STAs and the AP 102expects that the two or more STAs will have buffered data to betransmitted over the candidate subband (e.g., the two or more STAs haveindicated to the AP 102 that they have buffered data to be transmitted),the AP 102 may determine the candidate subband should be used only forUL MU-MIMO transmission.

According to the first embodiment of the present disclosure, in casethat a candidate subband is shared by two or more STAs and however theAP 102 is uncertain about how the candidate subband is used for the timebeing, the AP 102 may determine the candidate subband should be used forUL SU-MIMO or UL MU-MIMO transmission.

According to the first embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused only for UL SU-MIMO transmission by a STA, the AP 102 develops thetransmit beamforming matrices for the STA specific to UL SU-MIMOtransmission over the entire bandwidth or the candidate subband. Forexample, assume Hk represents the channel matrix of the communicationchannel from the STA to the AP 102 for the k-th tone (subcarrier). Thenthe transmit beamforming matrix Qk specific to UL SU-MIMO transmissionfor the k-th tone can be given by Qk=Vk, where Vk can be obtained viasingular value decomposition (SVD) of the channel matrix Hk.

According to the first embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused only for UL MU-MIMO transmission by a group of STAs, the AP 102develops the transmit beamforming matrices for each STA in the groupspecific to UL MU-MIMO transmission over the entire bandwidth or thecandidate subband. For example, assume a group of N STAs engage in ULMU-MIMO transmission over the entire bandwidth or the candidate subband,and Hk,i represents the channel matrix over the entire bandwidth or thecandidate subband for the i-th STA in the group and the k-th tone. Thenthe transmit beamforming matrices {Qk,i,i=1, 2 . . . , N} specific to ULMU-MIMO transmission for the k-th tone can be chosen in such a way that

(H _(k,i) Q _(k,i))^(H)(H _(k,j) Q _(k,j))=0

where i≠j and I, j=1, 2 . . . , N. Consequently, multiuser interferencein UL MU-MIMO transmission is suppressed and a simpler receiver can beused by the AP 102 to receive UL MU-MIMO transmission. As for theexample methods for determining the transmit beamforming matrices{Qk,i,i=1, 2 . . . , N} satisfying formula (1), please refer to[Transmit Beamforming and Detection Design for Uplink Multiuser MIMOSystem, Proceedings of Fortieth Asilomar Conference on Signals, Systemsand Computers, 2006 (ACSSC '06), Page 1593-1600].

According to the first embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused for UL SU-MIMO transmission by a STA or UL MU-MIMO transmission bya group of STAs, the AP 102 develops both the transmit beamformingmatrices for the STA specific to UL SU-MIMO transmission and thetransmit beamforming matrices for each STA in the group specific to ULMU-MIMO transmission over the entire bandwidth or the candidate subband.

During a time interval 426, the AP 102 transmits a feedback frame 406-1to the STA 104-1. After that, the AP 102 may sequentially transmitfeedback frames 406-2 and 406-3 to other STAs 104-2 and 104-3,respectively. For example, the AP 102 sends a feedback frame 406-2 tothe STA 104-2. The STAs 104 obtain respective transmit beamformingmatrices directly from the data of the respective feedback frames 406for UL MU transmission,

According to the first embodiment of the present disclosure, thefeedback frame 406 for a particular STA includes one or more of (i)indications of one or more candidate subbands for the particular STA;(ii) intended usage of transmission scheme corresponding to each of theone or more candidate subbands for the particular STA; (iii) one or morequality indicators corresponding to each of the one or more candidatesubbands for the particular STA; (iv) beamforming feedback correspondingto each of the one or more candidate subbands for the particular STA;(v) intended usage of transmission scheme corresponding to the entirebandwidth for the particular STA; (vi) one or more quality indicatorscorresponding to the entire bandwidth for the particular STA; (vii)beamforming feedback information corresponding to the entire bandwidthfor the particular STA; and (viii) UL power control information (e.g.required power adjustment amount), etc.

According to the first embodiment of the present disclosure, what isincluded in the beamforming feedback information corresponding to theentire bandwidth or a candidate subband for a particular STA depends onthe intended usage of transmission scheme for the entire bandwidth orthe candidate subband for the particular STA. If the entire bandwidth ora candidate subband should be used only for UL SU-MIMO transmission, thebeamforming feedback information corresponding to the entire bandwidthor the candidate subband shall represent the transmit beamformingmatrices specific to UL SU-MIMO transmission. If the entire bandwidth ora candidate subband should be used only for UL MU-MIMO transmission, thebeamforming feedback information corresponding to the entire bandwidthor the candidate subband shall represent the transmit beamformingmatrices specific to UL MU-MIMO transmission. If the entire bandwidth ora candidate subband should be used for UL SU-MIMO or UL MU-MIMOtransmission, the beamforming feedback information corresponding to theentire bandwidth or the candidate subband shall represent both thetransmit beamforming matrices specific to UL SU-MIMO transmission andthe transmit beamforming matrices specific to UL MU-MIMO transmission.

According to the first embodiment of the present disclosure, if a firstSTA (e.g., the STA 104-1) and a second STA (e.g., the STA 104-2) engagein UL MU-MIMO transmission over the entire bandwidth or a particularsubband, the transmit beamforming matrices specific to UL MU-MIMOtransmission over the entire bandwidth or the particular subband whichis represented in the feedback frame for the first STA (e.g., thefeedback frame 406-1 for the STA 104-1) are developed based. Thetransmit beamforming matrices specific to UL MU-MIMO transmission aredeveloped on not only the sounding frame transmitted by the first STA(e.g., the sounding frame 404-1 transmitted by the STA 104-1) but alsothe sounding frame transmitted by the second STA (e.g., the soundingframe 404-2 transmitted by the STA 104-2). In other words, the transmitbeamforming matrices specific to UL MU-MIMO transmission represented inthe feedback frame for the first STA (e.g., the feedback frame 406-1 forthe STA 104-1) vary when the channel state between the AP 102 and thesecond STA (e.g., the STA 104-2) has changed, even if the channel statebetween the AP 102 and the first STA (e.g., the STA 104-1) has notchanged.

FIG. 5 is a diagram illustrating an example feedback frame 500 that theAP 102 is configured to transmit to a STA during the sounding procedure400 of FIG. 4. The feedback frame 500 corresponds to each of thefeedback frames 406-1, 406-2 and 406-3 of FIG. 4. The feedback frame 500includes a MIMO control field 502, a wholeband feedback portion 504 anda subband feedback portion 506.

The wholeband feedback portion 504 includes a power control informationfield 512, an average SNR field 514, an intended usage field 516 and abeamforming feedback field 518. The wholeband feedback portion 504includes feedback that covers the entire bandwidth of the communicationchannel. Alternatively, the wholeband feedback portion 504 includesfeedback that covers the bandwidth of the sounding frame based on whichthe feedback was generated by the AP 102. The beamforming feedback field518 includes some form of beamforming feedback over the entire bandwidthfor a particular STA generated by the AP 102 based on a sounding frametransmitted by the particular STA. As abovementioned, the beamformingfeedback over the entire bandwidth depends on the transmission schemeintended to be used for the entire bandwidth. The beamforming feedbackfield 518 includes compressed beamforming feedback similar to what isdefined in the IEEE 802.11ac standard. Alternatively, the beamformingfeedback field 518 includes another suitable form of beamformingfeedback, such as uncompressed beamforming feedback similar to what isdefined in the IEEE 802.11n standard.

The subband feedback portion 506 includes a number of candidate subbandsfield 522 and a plurality of subband based feedback fields 524, each ofwhich corresponds to a specific candidate subband. Each of the subbandbased feedback fields 524 includes a subband indication field 532, anaverage SNR per subband field 534, an intended usage per subband field536 and a beamforming feedback per subband field 538. The subbandindication field 532 indicates a particular subband. The beamformingfeedback per subband field 538 includes some form of beamformingfeedback over the particular subband for a particular STA generated bythe AP 102 based on a sounding frame transmitted by the particular STA.As abovementioned, the beamforming feedback over a particular subbanddepends on the transmission scheme intended to be used for theparticular subband as specified in the corresponding intended usage persubband field 536. The beamforming feedback per subband field 538includes compressed beamforming feedback similar to what is defined inthe IEEE 802.11ac standard. Alternatively, the beamforming feedback persubband field 516 includes another suitable form of beamformingfeedback, such as uncompressed beamforming feedback similar to what isdefined in the IEEE 802.11n standard.

During a time interval 428 in FIG. 4, based on the channel stateinformation corresponding to the entire bandwidth, the qualityindicators corresponding to the one or more subbands of thecommunication channel and/or data buffer status obtained for at leastsome of the STAs 104, the AP 102 selects a subset of STAs for inclusioninto an UL group (e.g., STAs 104-1 and 104-2 in this example) for UL MUtransmission. The AP 102 shall also designate respective transmissionschemes and allocate respective transmission resources (e.g., subbandsin terms of UL OFDMA) to the STAs in the UL group.

For one example, in case that two or more STAs have indicated to the AP102 that they have a large amount of buffered data to be transmitted andquality of the communication channel for each of the two or more STAs isacceptable (e.g., SNR corresponding to the entire bandwidth exceeds to apredetermined threshold), the AP 102 may select the two or more STAs forinclusion into an UL group and schedule the two or more STAs in the ULgroup to perform UL MU-MIMO transmission over the entire bandwidth.

For another example, in case that two or more STAs have indicated to theAP 102 that they have buffered data to be transmitted and qualitycorresponding to one or more candidate subbands for each of the two ormore STAs is acceptable (e.g., SINR corresponding to the candidatesubband exceeds to a predetermined threshold), the AP 102 may select thetwo or more STAs for inclusion into an UL group. Then, the AP 102 mayallocate respective subbands to the two or more STAs in the UL group andschedule the two or more STAs in the UL group to perform UL SU-MIMOtransmission over their respective allocated subbands.

According to the first embodiment of the present disclosure, the timingorder of feedback transmission (time intervals 426) and grouping andsubband allocation (time interval 428) in FIG. 4 may be interchangeable.For example, during a time interval 426, the AP 102 may select a subsetof STAs for inclusion into an UL group, designate respectivetransmission schemes and allocate respective transmission resources toeach of the STAs in the UL group first. Then during a time interval 428,the AP 102 proceeds to transmitting respective feedback frames 406 tothe STAs 104 in the UL group.

During a time interval 432, the AP 102 transmits a trigger frame 408 tothe STAs included in the UL group (e.g., STAs 104-1 and 104-2 in thisexample) for UL MU transmission. The trigger frame 408 prompts the STAsin the UL group to simultaneously transmit data to the AP 102 at aparticular time interval. The trigger frame 408 also includesinformation on the designated transmission scheme and/or the allocatedtransmission resource for each of the STAs in the UL group.

During a time interval 434, if the trigger frame 408 triggers an ULMU-MIMO transmission, the STAs in the UL group (e.g., STAs 104-1 and104-2 in this example) transmit respective data 410 simultaneously overthe entire bandwidth to the AP 102 using respective transmit beamformingmatrices specific to UL MU-MIMO transmission over the entire bandwidth.If the trigger frame 408 triggers an UL OFDMA transmission, the STAs inthe UL group transmit respective data 410 simultaneously to the AP 102over respective allocated subbands using respective transmit beamformingmatrices. These transmit beamforming matrices can be generated fromrespective feedback frames 406 according to the respective designatedtransmission schemes and the respective allocated subbands. For example,if the designated transmission scheme for the STA 104-1 is UL SU-MIMO,the transmit beamforming matrices specific to UL SU-MIMO transmissionover the allocated subband for the STA 104-1 are generated directly fromthe corresponding data of the feedback frame 406-1.

Second Embodiment

FIG. 6 is a schematic timing diagram illustrating an example soundingprocedure 600 and an example UL MU transmission based on the soundingprocedure 600, according to a second embodiment of the presentdisclosure. Similar to the sounding procedure 400 in FIG. 4, thesounding procedure 600 is also an explicit sounding procedure.

During a time interval 622-1, the AP 102 transmits a soundingannouncement frame 602-1 to the STA 104-1 to initiate the soundingprocedure 600 and request the STA 104-1 to transmit a sounding frame.During a time interval 624-1, in response to receiving the soundingannouncement frame 602-1, the STA 104-1 sends a sounding frame 604-1 tothe AP 102. The sounding frame 604-1 includes suitable training signalsin the PHY preamble (e.g., HE-LTF field). The sounding frame 604-1 mayalso include UL power control information for the STA 104-1 (e.g.,transmit power, power adjustable range and/or power headroom) in the PHYpreamble (e.g., HE-SIG-A field). The sounding frame 604-1 may be a NDP.The AP 102 obtains, based on training signals included in the soundingframe 604-1, channel state information (e.g., gain, phase, SNR, etc.)corresponding to the entire bandwidth of the communication channel fromthe STA 104-1 to the AP 102. Additionally or alternatively, the AP 102determines quality indicators (e.g., SNR, SNIR, signal strength, etc.)corresponding to one or more subbands of the communication channel fromthe STA 104-1 to the AP 102. The AP 102 further identifies one or morecandidate subbands for the STA 104-1 to be used for UL transmission.

The AP 102 may sequentially prompt other STAs 104 to transmit respectivesounding frames. Based on the received sounding frames, the AP 102obtains channel state information corresponding to the entire bandwidthof the communication channel from each of other STAs 104 to the AP 102and/or quality indicators corresponding to one or more subbands of thecommunication channel from each of other STAs 104 to the AP 102. The AP102 further identifies one or more candidate subbands for each of theother STAs 104. For example, during a time interval 622-2, the AP 102sends a sounding announcement frame 602-2 to the STA 104-2. During atime interval 624-2, in response to receiving the sounding announcementframe 602-2, the STA 104-2 sends a sounding frame 604-2 to the AP 102.The AP 102 obtains channel state information corresponding to the entirebandwidth of the communication channel from the STA 104-2 to the AP 102.Additionally or alternatively, the AP 102 determines quality indicatorscorresponding to each of the one or more subbands of the communicationchannel from the STA 104-2 to the AP 102. Furthermore, the AP 102identifies one or more candidate subbands for the STA 104-2 to be usedfor UL transmission.

According to the second embodiment of the present disclosure, the AP 102identifies intended usage of transmission scheme for the entirebandwidth and/or each of the one or more candidate subbands for each ofthe STAs 104 based on channel state information corresponding to theentire bandwidth of the communication channel from each of the STAs 104to the AP 102 and/or quality indicators corresponding to the one or morecandidate subbands of the communication channel from each of the STAs104 to the AP 102. For example, the AP 102 determines whether the entirebandwidth or each of the one or more candidate subbands for each of theSTA 104 should be used for UL SU-MIMO transmission, UL MU-MIMOtransmission or both.

According to the second embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused only for UL SU-MIMO transmission by a STA, the AP 102 develops thetransmit beamforming matrices for the STA specific to UL SU-MIMOtransmission over the entire bandwidth or the candidate subband in asimilar manner to the first embodiment,

According to the second embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused only for UL MU-MIMO transmission by a group of STAs, the AP 102develops the transmit beamforming matrices for each STA in the groupspecific to UL MU-MIMO transmission over the entire bandwidth or thecandidate subband in a similar manner to the first embodiment.

According to the second embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused for UL SU-MIMO transmission by a STA or UL MU-MIMO transmission bya group of STAs, the AP 102 develops both the transmit beamformingmatrices for the STA specific to UL SU-MIMO transmission and thetransmit beamforming matrices for each STA in the group specific to ULMU-MIMO transmission over the entire bandwidth or the candidate subband.

During a time interval 626, the AP 102 transmits respective feedbackframes 606 to the STAs 104 simultaneously in a DL MU PPDU bymultiplexing the feedback frames with DL OFDMA or DL MU-MIMO. In thisexample, the AP 102 transmits the feedback frames 606-1, 606-2 and 606-3to the STAs 104-1, 104-2 and 104-3, respectively, in a DL MU PPDU. Notethat the transmit beamforming matrices to be used by the AP 102 for eachof the STAs 104 in DL MU transmission shall be obtained in advance via asounding procedure for DL MU transmission (see U.S. Patent ApplicationNo. 2015/0146807A1 for example). The STAs 104 obtains the respectivetransmit beamforming matrices directly from the data of the respectivefeedback frames 606 for UL MU transmission.

According to the second embodiment of the present disclosure, since thefeedback frames 606 are transmitted by the AP 102 simultaneously to theSTAs 104, channel efficiency is improved compared to the firstembodiment where the feedback frames 406 are transmitted by the AP 102sequentially to the STAs 104.

According to the second embodiment of the present disclosure, thefeedback frame 606 for a particular STA includes one or more of (i)indications of one or more candidate subbands for the particular STA;(ii) intended usage of transmission scheme corresponding to each of theone or more candidate subbands for the particular STA; (iii) one or morequality indicators corresponding to each of the one or more candidatesubbands for the particular STA; (iv) beamforming feedback correspondingto each of the one or more candidate subbands for the particular STA;(v) intended usage of transmission scheme corresponding to the entirebandwidth for the particular STA; (vi) one or more quality indicatorscorresponding to the entire bandwidth for the particular STA; (vii)beamforming feedback corresponding to the entire bandwidth for theparticular STA; and (viii) power control information (e.g. requiredpower adjustment amount), etc.

According to the second embodiment of the present disclosure, what isincluded in the beamforming feedback corresponding to the entirebandwidth or a candidate subband for a particular STA depends on theintended usage of transmission scheme for the entire bandwidth or thecandidate subband for the particular STA. If the entire bandwidth or acandidate subband intends to be used only for UL SU-MIMO transmission,the beamforming feedback corresponding to the entire bandwidth or thecandidate subband shall represent the transmit beamforming matricesspecific to UL SU-MIMO transmission. If the entire bandwidth or acandidate subband intends to be used only for UL MU-MIMO transmission,the beamforming feedback corresponding to the entire bandwidth or thecandidate subband shall represent the transmit beamforming matricesspecific to UL MU-MIMO transmission. If the entire bandwidth or acandidate subband intends to be used for UL SU-MIMO or UL MU-MIMOtransmission, the beamforming feedback corresponding to the entirebandwidth or the candidate subband shall represent both the transmitbeamforming matrices specific to UL SU-MIMO transmission and thetransmit beamforming matrices specific to UL MU-MIMO transmission.

During a time interval 628, based on channel state informationcorresponding to the entire bandwidth, quality indicators correspondingto the one or more subbands of the communication channel and/or databuffer status obtained for at least some of the STAs 104, the AP 102selects a subset of STAs for inclusion into an UL group for UL MUtransmission. The AP 102 shall also designate respective transmissionschemes and allocate respective transmission resources (e.g., subbandsin terms of UL OFDMA) to the STAs in the UL group.

According to the second embodiment of the present disclosure, the timingorder of feedback transmission (time intervals 626) and grouping andsubband allocation (time interval 628) in FIG. 6 may be interchangeable.For example, during a time interval 626, the AP 102 may select STAsinclusion into an UL group, designate respective transmission schemesand allocate respective transmission resources to the STAs in the ULgroup first. Then during a time interval 628, the AP 102 proceeds totransmitting respective feedback frames 606 to the STAs 104 in the ULgroup.

During a time interval 632, the AP 102 transmits a trigger frame 608 tothe STAs in the UL group (e.g., STAs 104-1 and 104-2 in this example)for UL MU transmission. The trigger frame 608 prompts the STAs in the ULgroup to simultaneously transmit data to the AP 102 at a particulartime. The trigger frame 608 also includes information on the designatedtransmission scheme and/or the allocated transmission resource for eachof the STAs in the UL group.

During a time interval 634, if the trigger frame 608 triggers an ULMU-MIMO transmission, the STAs in the UL group (i.e., STAs 104-1 and104-2 in this example) transmit respective data 610 simultaneously overthe entire bandwidth to the AP 102 using respective transmit beamformingmatrices specific to UL MU-MIMO transmission over the entire bandwidth.If the trigger frame 608 triggers an UL OFDMA transmission, the STAs inthe UL group transmit respective data 610 simultaneously to the AP 102over respective allocated subbands using respective transmit beamformingmatrices which can be generated from respective feedback frames 606according to the respective designated transmission schemes and therespective allocated subbands. For example, if the designatedtransmission scheme for the STA 104-1 is UL SU-MIMO, the transmitbeamforming matrices specific to UL SU-MIMO transmission over theallocated subband for the STA 104-1 are generated directly from thecorresponding data of the feedback frame 606-1.

Third Embodiment

FIG. 7 is a schematic timing diagram illustrating an example soundingprocedure 700 and an example UL MU transmission based on the soundingprocedure 700, according to a third embodiment of the presentdisclosure. Similar to the sounding procedure 400 in FIG. 4, thesounding procedure 700 is also an explicit sounding procedure.

During a time interval 722, the AP 102 transmits a sounding announcementframe 702 to the STAs 104 to initiate the sounding procedure 700. Inother words, a single sounding announcement frame 702 is multicasted toall the STAs 104. The sounding announcement frame 702 containsinformation to coordinate the timing when the STAs 104 transmitrespective sounding frames. For example, payload of the soundingannouncement frame 702 can indicate an ordering of the STAs 104 that arerequested to transmit sounding frames.

According to the third embodiment of the present disclosure, since thesounding announcement frame 702 is multicasted to the STAs 104, channelefficiency is improved compared to the second embodiment where thesounding announcement frames 602 are transmitted by the AP 102individually to the STAs 104.

During a time interval 724, in response to receiving the soundingannouncement frame 702, the STAs 104 sequentially transmit respectivesounding frames 704 to the AP 102 according to the timing informationincluded in the sounding announcement frame 702. In this example, theSTA 104-1 sends a sounding frame 704-1 to the AP 102, followed by theSTA 104-2 and the STA 104-3. Each of the sounding frames 704 includessuitable training signals in the PHY preamble (e.g., HE-LTF field). Eachof the sounding frames 704 may also include UL power control informationfor the STA 104 transmitting the sounding frame (e.g., transmit power,power adjustable range and/or power headroom) in the PHY preamble (e.g.,HE-SIG-A field). Each of the sounding frames 704 may be a NDP. The AP102 obtains, based on training signals included in each of the soundingframes 704, channel state information (e.g., gain, phase, SNR, etc.)corresponding to the entire bandwidth of the communication channel fromeach of the STAs 104 to the AP 102. Additionally or alternatively, theAP 102 determines quality indicators (e.g., SNR, SNIR, signal strength,etc.) corresponding to each of one or more subbands of the communicationchannel from each of the STAs 104 to the AP 102. The AP 102 furtheridentifies one or more candidate subbands for each of the STAs 104 to beused for UL transmission.

According to the third embodiment of the present disclosure, based onthe channel state information corresponding to the entire bandwidth ofthe communication channel from each of the STAs 104 to the AP 102 and/orquality indicators corresponding to the one or more candidate subbandsof the communication channel from each of the STAs 104 to the AP 102,the AP 102 identifies intended usage of transmission scheme for theentire bandwidth and/or each of the one or more candidate subbands foreach of the STAs 104. For example, the AP 102 determines whether theentire bandwidth or each of the one or more candidate subbands for eachof the STA 104 should be used for UL SU-MIMO transmission, UL MU-MIMOtransmission or both.

According to the third embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused only for UL SU-MIMO transmission by a STA, the AP 102 develops thetransmit beamforming matrices for the STA specific to UL SU-MIMOtransmission over the entire bandwidth or the candidate subband in asimilar manner to the first embodiment.

According to the third embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused only for UL MU-MIMO transmission by a group of STAs, the AP 102develops the transmit beamforming matrices for each STA in the UL groupspecific to UL MU-MIMO transmission over the entire bandwidth or thecandidate subband in a similar manner to the first embodiment.

According to the third embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused for UL SU-MIMO transmission by a STA or UL MU-MIMO transmission bya group of STAs, the AP 102 develops both the transmit beamformingmatrices specific to UL SU-MIMO transmission for the STA and thetransmit beamforming matrices specific to UL MU-MIMO transmission foreach STA in the group over the entire bandwidth or the candidatesubband.

During a time interval 726, the AP 102 transmits respective feedbackframes 706 to the STAs 104 simultaneously in a DL MU PPDU. In thisexample, the AP 102 transmits the feedback frames 706-1, 706-2 and 706-3to the STAs 104-1, 104-2 and 104-3, respectively, in a DL MU PPDU. Notethat the transmit beamforming matrices to be used by the AP 102 for eachof the STAs 104 in DL MU transmission shall be obtained in advance via asounding procedure for DL MU transmission. The STAs 104 obtains therespective transmit beamforming matrices directly from the data of therespective feedback frames 706 for UL MU transmission.

According to the third embodiment of the present disclosure, thefeedback frame 706 for a particular STA includes one or more of (i)indications of one or more candidate subbands for the particular STA;(ii) intended usage of transmission scheme corresponding to each of theone or more candidate subbands for the particular STA; (iii) one or morequality indicators corresponding to each of the one or more candidatesubbands for the particular STA; (iv) beamforming feedback correspondingto each of the one or more candidate subbands for the particular STA;(v) intended usage of transmission scheme corresponding to the entirebandwidth for the particular STA; (vi) one or more quality indicatorscorresponding to the entire bandwidth for the particular STA; (vii)beamforming feedback corresponding to the entire bandwidth for theparticular STA; and (viii) power control information (e.g. requiredpower adjustment amount), etc.

According to the third embodiment of the present disclosure, what isincluded in the beamforming feedback corresponding to the entirebandwidth or a candidate subband for a particular STA depends on theintended usage of transmission scheme for the entire bandwidth or thecandidate subband for the particular STA. If the entire bandwidth or acandidate subband intends to be used only for UL SU-MIMO transmission,the beamforming feedback corresponding to the entire bandwidth or thecandidate subband shall represent the transmit beamforming matricesspecific to UL SU-MIMO transmission. If the entire bandwidth or acandidate subband should be used only for UL MU-MIMO transmission, thebeamforming feedback corresponding to the entire bandwidth or thecandidate subband shall represent the transmit beamforming matricesspecific to UL MU-MIMO transmission. If the entire bandwidth or acandidate subband should be used for UL SU-MIMO or UL MU-MIMOtransmission, the beamforming feedback corresponding to the entirebandwidth or the candidate subband shall represent both the transmitbeamforming matrices specific to UL SU-MIMO transmission and thetransmit beamforming matrices specific to UL MU-MIMO transmission.

During a time interval 728, the AP 102 selects STAs for inclusion intoan UL group for UL MU transmission based on the channel stateinformation corresponding to the entire bandwidth and/or qualityindicators corresponding to the one or more subbands of thecommunication channel obtained for at least some of the STAs 104. The AP102 shall also designate respective transmission schemes and allocaterespective transmission resources (e.g., subbands in terms of UL OFDMA)to the STAs in the UL group.

According to the third embodiment of the present disclosure, the timingorder of feedback transmission (time intervals 726) and grouping andsubband allocation (time interval 728) in FIG. 7 may be interchangeable.For example, during a time interval 726, the AP 102 may select STAsinclusion into an UL group, designate respective transmission schemesand allocate respective transmission resources to the STAs in the ULgroup first. Then during a time interval 728, the AP 102 proceeds totransmit respective feedback frames 706 to the STAs 104.

During a time interval 732, the AP 102 transmits a trigger frame 708 tothe STAs in the UL group (e.g., STAs 104-1 and 104-2 in this example)for UL MU transmission. The trigger frame 708 prompts the STAs in the ULgroup to simultaneously transmit data to the AP 102 at a particulartime. The trigger frame 708 also includes information on the designatedtransmission scheme and/or the allocated transmission resource for eachof the STAs in the UL group.

During a time interval 734, if the trigger frame 708 triggers an ULMU-MIMO transmission, the STAs in the UL group (i.e., STAs 104-1 and104-2 in this example) transmit respective data 710 simultaneously overthe entire bandwidth to the AP 102 using respective transmit beamformingmatrices specific to UL MU-MIMO transmission over the entire bandwidth.If the trigger frame 708 triggers an UL OFDMA transmission, the STAs inthe UL group transmit respective data 710 simultaneously to the AP 102over respective allocated subbands using respective transmit beamformingmatrices which can be generated from respective feedback frames 706according to the respective designated transmission schemes and therespective allocated subbands. For example, if the designatedtransmission scheme for the STA 104-1 is UL SU-MIMO, the transmitbeamforming matrices specific to UL SU-MIMO transmission over theallocated subband for the STA 104-1 are generated directly from thecorresponding data of the feedback frame 706-1.

Fourth Embodiment

FIG. 8 is a schematic timing diagram illustrating an example soundingprocedure 800 and an example UL MU transmission based on the soundingprocedure 800, according to a fourth embodiment of the presentdisclosure. Similar to the sounding procedure 400 of FIG. 4, thesounding procedure 800 is also an explicit sounding procedure.

During a time interval 822, the AP 102 transmits a sounding announcementframe 802 to the STAs 104 to initiate the sounding procedure 800. Thesounding announcement frame 802 contains information to coordinate thetiming when the STAs 104 transmit respective sounding frames. Forexample, payload of the sounding announcement frame 802 can indicate anordering of the STAs 104 that are requested to transmit sounding frames.

During a time interval 824, in response to receiving the soundingannouncement frame 802, the STAs 104 sequentially transmit respectivesounding frames 804 to the AP 102 according to the timing informationincluded in the sounding announcement frame 802. In this example, theSTA 104-1 sends a sounding frame 804-1 to the AP 102, followed by theSTA 104-2 and the STA 104-3. Each of the sounding frames 804 includessuitable training signals in the PHY preamble (e.g., HE-LTF field). Eachof the sounding frames 804 may also include UL power control informationfor the STA 104 transmitting the sounding frame (e.g., transmit power,power adjustable range and/or power headroom) in the PHY preamble (e.g.,HE-SIG-A field). Each of the sounding frames 804 may be a NDP. The AP102 obtains, based on training signals included in each of the soundingframes 804, channel state information (e.g., gain, phase, SNR, etc.)corresponding to the entire bandwidth of the communication channel fromeach of the STAs 104 to the AP 102. Additionally or alternatively, theAP 102 determines quality indicators (e.g., SNR, SNIR, signal strength,etc.) corresponding to each of one or more subbands of the communicationchannel from each of the STAs 104 to the AP 102. The AP 102 furtheridentifies one or more candidate subbands for each of the STAs 104 to beused for UL transmission.

According to the fourth embodiment of the present disclosure, the AP 102identifies intended usage of transmission scheme for the entire channelbandwidth and/or each of the one or more candidate subbands for each ofthe STAs 104 based on the channel state information corresponding to theentire bandwidth of the communication channel from each of the STAs 104to the AP 102 and/or quality indicators corresponding to the one or morecandidate subbands of the communication channel from each of the STAs104 to the AP 102. For example, the AP 102 determines whether the entirebandwidth or each of the one or more candidate subbands for each of theSTA 104 should be used for UL SU-MIMO transmission, UL MU-MIMOtransmission or both.

According to the fourth embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused only for UL SU-MIMO transmission by a STA, the AP 102 develops thetransmit beamforming matrices for the STA specific to UL SU-MIMOtransmission over the entire bandwidth or the candidate subband in asimilar manner to the first embodiment.

According to the fourth embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused only for UL MU-MIMO transmission by a group of STAs, the AP 102develops the transmit beamforming matrices for each STA in the groupspecific to UL MU-MIMO transmission over the entire bandwidth or thecandidate subband in a similar manner to the first embodiment.

According to the fourth embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused for UL SU-MIMO transmission by a STA or UL MU-MIMO transmission bya group of STAs, the AP 102 develops both the transmit beamformingmatrices for the STA specific to UL SU-MIMO transmission and thetransmit beamforming matrices for each STA in the group specific to ULMU-MIMO transmission over the entire bandwidth or the candidate subband.

During a time interval 826, the AP 102 selects STAs for inclusion intoan UL group for UL MU transmission based on the channel stateinformation corresponding to the entire bandwidth and/or qualityindicators corresponding to the one or more subbands of thecommunication channel obtained for at least some of the STAs 104. The AP102 shall also designate respective transmission schemes and allocaterespective transmission resources (e.g., subbands in terms of UL OFDMA)to the STAs in the UL group.

During a time interval 828, the AP 102 transmits respective feedbackframes 806 to the STAs 104 in the UL group simultaneously in a DL MUPPDU. The AP 102 also transmits respective trigger frames 808 to theSTAs in the UL group (e.g., STAs 104-1 and 104-2 in this example) in thesame DL MU PPDU. In this example, the AP 102 transmits an aggregation ofthe feedback frame 806-1 and the trigger frame 808-1, an aggregation ofthe feedback frame 806-2 and the trigger frame 808-2, and the feedbackframe 806-3 to the STAs 104-1, 104-2 and 104-3, respectively, in a DL MUPPDU. Note that the transmit beamforming matrices to be used by the AP102 for each of the STAs 104 in DL MU transmission shall be obtained inadvance via a sounding procedure for DL MU transmission. The STAs 104obtains the respective transmit beamforming matrices directly from thedata of the respective feedback frames 806 for UL MU transmission.

According to the fourth embodiment of the present disclosure, since thetrigger frames 808 and the feedback frames 806 are transmitted to theSTAs in the UL group in the same DL MU PPDU, the channel efficiency isimproved compared to the third embodiment where the trigger frame 708and the feedback frames 706 are transmitted by the AP 102 separately tothe STAs in the UL group.

According to the fourth embodiment of the present disclosure, each ofthe trigger frames 808 prompts a particular STA in the UL group totransmit data to the AP 102 at a particular time. Each of the triggerframes 808 also includes information on the designated transmissionscheme and/or the allocated transmission resource for a particular STAin the UL group.

According to the fourth embodiment of the present disclosure, thefeedback frame 806 for a particular STA includes one or more of (i)indications of one or more candidate subbands for the particular STA;(ii) intended usage of transmission scheme corresponding to each of theone or more candidate subbands for the particular STA; (iii) one or morequality indicators corresponding to each of the one or more candidatesubbands for the particular STA; (iv) beamforming feedback correspondingto each of the one or more candidate subbands for the particular STA;(v) intended usage of transmission scheme corresponding to the entirebandwidth for the particular STA; (vi) one or more quality indicatorscorresponding to the entire bandwidth for the particular STA; (vii)beamforming feedback corresponding to the entire bandwidth for theparticular STA; and (viii) power control information (e.g. requiredpower adjustment amount), etc.

According to the fourth embodiment of the present disclosure, what isincluded in the beamforming feedback corresponding to the entirebandwidth or a candidate subband for a particular STA depends on theintended usage of transmission scheme for the entire bandwidth or thecandidate subband for the particular STA. If the entire bandwidth or acandidate subband should be used only for UL SU-MIMO transmission, thebeamforming feedback corresponding to the entire bandwidth or thecandidate subband shall represent the transmit beamforming matricesspecific to UL SU-MIMO transmission. If the entire bandwidth or acandidate subband should be used only for UL MU-MIMO transmission, thebeamforming feedback corresponding to the entire bandwidth or thecandidate subband shall represent the transmit beamforming matricesspecific to UL MU-MIMO transmission. If the entire bandwidth or acandidate subband should be used for UL SU-MIMO or UL MU-MIMOtransmission, the beamforming feedback corresponding to the entirebandwidth or the candidate subband shall represent both the transmitbeamforming matrices specific to UL SU-MIMO transmission and thetransmit beamforming matrices specific to UL MU-MIMO transmission.

During a time interval 832, if the trigger frames 808 trigger an ULMU-MIMO transmission, the STAs in the UL group (i.e., STAs 104-1 and104-2 in this example) transmit respective data 810 simultaneously tothe AP 102 over the entire bandwidth using respective transmitbeamforming matrices specific to UL MU-MIMO transmission over the entirebandwidth. If the trigger frames 808 trigger an UL OFDMA transmission,the STAs in the UL group transmit respective data 810 simultaneously tothe AP 102 over respective allocated subbands using respective transmitbeamforming matrices. These transmit beamforming matrices can begenerated from respective feedback frames 806 according to therespective designated transmission schemes and the respective allocatedsubbands. For example, if the designated transmission scheme for the STA104-1 is UL SU-MIMO, the transmit beamforming matrices specific to ULSU-MIMO transmission over the allocated subband for the STA 104-1 aregenerated directly from the corresponding data of the feedback frame806-1.

Fifth Embodiment

FIG. 9 is a schematic timing diagram illustrating an example soundingprocedure 900 and an example UL MU transmission based on the soundingprocedure 900, according to a fifth embodiment of the presentdisclosure. Similar to the sounding procedure 400 of FIG. 9, thesounding procedure 900 is also an explicit sounding procedure.

During a time interval 922, the AP 102 transmits a sounding announcementframe 902 to the STAs 104 to initiate the sounding procedure 900. Thesounding announcement frame 902 contains information to coordinate thetiming when the STAs 104 transmit respective sounding frames. Forexample, payload of the sounding announcement frame 902 can indicate anordering of the STAs 104 that are requested to transmit sounding frames.

During a time interval 924, in response to receiving the soundingannouncement frame 902, the STAs 104 sequentially transmit respectivesounding frames 904 to the AP 102 according to the timing informationincluded in the sounding announcement frame 902. In this example, theSTA 104-1 sends a sounding frame 904-1 to the AP 102, followed by theSTA 104-2 and the STA 104-3. Each of the sounding frames 904 includessuitable training signals in the PHY preamble (e.g., HE-LTF field). Eachof the sounding frames 904 may also include UL power control informationfor the STA 104 transmitting the sounding frame (e.g., transmit power,power adjustable range and/or power headroom) in the PHY preamble (e.g.,HE-SIG-A field). Each of the sounding frames 904 may be a NDP. The AP102 obtains, based on training information included in each of thesounding frames 904, channel state information (e.g., gain, phase, SNR,etc.) corresponding to the entire bandwidth of the communication channelfrom each of the STAs 104 to the AP 102. Additionally or alternatively,the AP 102 determines quality indicators (e.g., SNR, SNIR, signalstrength, etc.) corresponding to each of one or more subbands of thecommunication channel from each of the STAs 104 to the AP 102. The AP102 further identifies one or more candidate subbands for each of theSTAs 104 to be used for UL transmission.

According to the fifth embodiment of the present disclosure, based onthe channel state information corresponding to the entire bandwidth ofthe communication channel from each of the STAs 104 to the AP 102 and/orquality indicators corresponding to the one or more subbands of thecommunication channel from each of the STAs 104 to the AP 102, the AP102 identifies intended usage of transmission scheme for the entirebandwidth and/or each of the one or more candidate subbands for each ofthe STAs 104. For example, the AP 102 determines whether the entirebandwidth or each of the candidate subbands for each of the STA 104 thatshould be used for UL SU-MIMO transmission, UL MU-MIMO transmission orboth.

According to the fifth embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband of thecommunication channel from a STA to the AP 102 should be used only forUL SU-MIMO transmission by a STA, the AP 102 calculates the transmitbeamforming matrices for the STA specific to UL SU-MIMO transmissionover the entire bandwidth or the candidate subband in a similar mannerto the first embodiment.

According to the fifth embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused only for UL MU-MIMO transmission by a group of STAs, the AP 102calculates the transmit beamforming matrices for each STA in the groupspecific to UL MU-MIMO transmission over the entire bandwidth or thecandidate subband in a similar manner to the first embodiment.

According to the fifth embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused for UL SU-MIMO transmission by a STA or UL MU-MIMO transmission bya group of STAs, the AP 102 calculates both the transmit beamformingmatrices for the STA specific to UL SU-MIMO transmission and thetransmit beamforming matrices for each STA in the group specific to ULMU-MIMO transmission over the entire bandwidth or the candidate subband.

During a time interval 926, the AP 102 selects STAs for inclusion intoan UL group for UL MU transmission based on the channel stateinformation corresponding to the entire bandwidth, quality indicatorscorresponding to the one or more subbands of the communication channeland/or data buffer status obtained for at least some of the STAs 104.The AP 102 shall also designate respective transmission schemes andallocate respective transmission resources (e.g., subbands in terms ofUL OFDMA) to the STAs in the UL group.

During a time interval 928, the AP 102 transmits respective feedbackframes 906 to the STAs 104 in the UL group simultaneously in a DL MUPPDU. In this example, the AP 102 transmits the feedback frames 906-1,906-2 and 906-3 to the STAs 104-1, 104-2 and 104-3, respectively, in aDL MU PPDU. Note that the transmit beamforming matrices to be used bythe AP 102 for each of the STAs 104 in DL MU transmission shall beobtained in advance via a sounding procedure for DL MU transmission. TheSTAs 104 obtain the respective transmit beamforming matrices directlyfrom the data of the respective feedback frames 906 for UL MUtransmission.

According to the fifth embodiment of the present disclosure, thefeedback frame 806 for a particular STA includes one or more of (i)indications of one or more candidate subbands for the particular STA;(ii) intended usage of transmission scheme corresponding to each of theone or more candidate subbands for the particular STA; (iii) one or morequality indicators corresponding to each of the one or more candidatesubbands for the particular STA; (iv) beamforming feedback correspondingto each of the one or more candidate subbands for the particular STA;(v) intended usage of transmission scheme corresponding to the entirebandwidth for the particular STA; (vi) one or more quality indicatorscorresponding to the entire bandwidth for the particular STA; (vii)beamforming feedback corresponding to the entire bandwidth for theparticular STA; and (viii) power control information (e.g. requiredpower adjustment amount), etc.

According to the fifth embodiment of the present disclosure, each of thefeedback frames for the STAs in the UL group (e.g., 906-1 or 906-2 inthis example) also contains trigger information to prompt a particularSTA in the UL group to transmit data to the AP 102 at a particular timeand inform the designated transmission scheme and/or the allocatedtransmission resource to a particular STA in the UL group.

According to the fifth embodiment of the present disclosure, since noseparate trigger frames are transmitted to the STAs in the UL group,channel efficiency is improved compared to the fourth embodiment wherethe separate trigger frames 808 are transmitted by the AP 102 to theSTAs in the UL group.

According to the fifth embodiment of the present disclosure, what isincluded in the beamforming feedback corresponding to the entirebandwidth or a candidate subband for a particular STA depends on theintended usage of transmission scheme for the entire bandwidth or thecandidate subband for the particular STA. If the entire bandwidth or acandidate subband should be used only for UL SU-MIMO transmission, thebeamforming feedback corresponding to the entire bandwidth or thecandidate subband shall represent the transmit beamforming matricesspecific to UL SU-MIMO transmission. If the entire bandwidth or acandidate subband should be used only for UL MU-MIMO transmission, thebeamforming feedback corresponding to the entire bandwidth or thecandidate subband shall represent the transmit beamforming matricesspecific to UL MU-MIMO transmission. If the entire bandwidth or acandidate subband should be used for UL SU-MIMO or UL MU-MIMOtransmission, the beamforming feedback corresponding to the entirebandwidth or the candidate subband shall represent both the transmitbeamforming matrices specific to UL SU-MIMO transmission and thetransmit beamforming matrices specific to UL MU-MIMO transmission.

During a time interval 932, if the trigger information included in thefeedback frames 906 triggers an UL MU-MIMO transmission, the STAs in theUL group (i.e., STAs 104-1 and 104-2 in this example) transmitrespective data 910 simultaneously to the AP 102 over the entirebandwidth using respective transmit beamforming matrices specific to ULMU-MIMO transmission over the entire bandwidth. If the triggerinformation included in the feedback frames 906 triggers an UL OFDMAtransmission, the STAs in the UL group transmit respective data 910simultaneously to the AP 102 over respective allocated subbands usingrespective transmit beamforming matrices which can be generated fromrespective feedback frames 906 according to the respective designatedtransmission schemes and the respective allocated subbands. For example,if the designated transmission scheme for the STA 104-1 is UL SU-MIMO,the transmit beamforming matrices specific to UL SU-MIMO transmissionover the allocated subband for the STA 104-1 are generated directly fromthe corresponding data of the feedback frame 906-1.

Sixth Embodiment

FIG. 10 is a schematic timing diagram illustrating an example soundingprocedure 1000 and an example cascaded DL and UL MU transmission basedon the sounding procedure 1000, according to a sixth embodiment of thepresent disclosure. Unlike the first five embodiments that addressexplicit UL sounding only, the sounding procedure 1000 is an explicitbidirectional sounding procedure in which explicit DL sounding andexplicit UL sounding are jointly performed in an efficient manner.

During a time interval 1022, the AP 102 transmits a soundingannouncement frame 1002 to the STAs 104 to initiate the soundingprocedure 1000. The sounding announcement frame 1002 containsinformation to identify the STAs 104 that are intended participants inthe sounding procedure 1000. For example, the sounding announcementframe 1002 identifies the STAs 104 by including a suitable identifier,such as at least a portion of an association identifier (AID),corresponding to each of the STAs 104 identified as an intendedparticipant.

During a time interval 1024, as a part of explicit DL sounding, the AP102 transmits a sounding frame 1004 that includes suitable trainingsignals in the PHY preamble (e.g., HE-LTF field) and may be a NDP. Eachof the STAs 104 identified by the sounding announcement frame 1002obtains, based on training signals included in the sounding frame 1004,DL channel state information (e.g., the gain, the phase and SNR, etc.)corresponding to the entire bandwidth of the communication channel fromthe AP 102 and the STA 104. Additionally or alternatively, each of theSTAs 104 determines DL quality indicators (e.g., SNR, SNIR, signalstrength, etc.) corresponding to each of one or more subbands of thecommunication channel from the AP 102 and the STA 104. The STA 104further identifies one or more preferred subbands, and determines anorder of preference of the identified preferred subbands for DLtransmission.

During a time interval 1026, as a part of explicit DL sounding, the STA104-1 that is identified first in the sounding announcement frame 1002transmits its feedback frame 1006-1. The AP 102 receives the feedbackframe 1006-1 from the STA 104-1 and then successively transmitsrespective feedback poll frames 1008 to each of the remaining STAs 104identified by the sounding announcement frame 1002 as participants inthe sounding procedure 1000. Each of the remaining STAs 104 transmitsits feedback frame 1006 accordingly.

A feedback frame 1006 from a particular STA includes one or more of (i)indications of one or more preferred subbands identified by theparticular STA; (ii) indications of order of preference of the one ormore preferred subbands identified by the particular STA; (iii) one ormore DL quality indicators corresponding to each of the one or morepreferred subbands identified by the particular STA; (iv) DL beamformingfeedback, corresponding to each of the one or more preferred subbandsidentified by the particular STA; (v) DL channel state informationcorresponding to the entire bandwidth of the communication channelbetween the AP 102 and the particular STA; (vi) one or more DL qualityindicators corresponding to the entire bandwidth of the communicationchannel from the AP 102 to the particular STA, and (vii) DL beamformingfeedback corresponding to the entire bandwidth of the communicationchannel from the AP 102 to the particular STA, etc. The beamformingfeedback may be a compressed beamforming feedback similar to what isdefined in the IEEE 802.11ac standard. Alternatively, the beamformingfeedback may be another suitable form of beamforming feedback, such asuncompressed beamforming feedback.

According to the sixth embodiment of the present disclosure, a feedbackframe 1006 for explicit DL sounding also functions as a sounding framefor explicit UL sounding. In other words, in addition to trainingsignals included in the PHY preamble (e.g., HE-LTF field) that are usedby the receiver for demodulating the data portion of the feedback frame1006, the feedback frame 1006 needs to include suitable additionaltraining signals in the PHY preamble (e.g., a new field immediatelyafter HE-LTF field) in order to provide additional reference for ULsounding so that the receiver can form an estimate of additionaldimensions of the channel beyond those that are used by the data portionof the feedback frame 1006. Each of the feedback frames 1006 may alsoinclude UL power control information for the STA transmitting thefeedback frame (e.g., transmit power, power adjustable range and/orpower headroom) in the PHY preamble (e.g., HE-SIG-A field).

Based on the feedback frames 1006 received by the AP 102 during the timeinterval 1026, the AP 102 obtains one or more DL quality indicators andDL transmit beamforming matrices corresponding to the entire bandwidthand/or one or more subbands of the communication channel from the AP 102to each of the STAs 104. For example, the AP 102 obtains the one or moreDL quality indicators and/or transmit beamforming matrices for aparticular STA 104 directly from the feedback frame 1006 received fromthe particular STA 104. Alternatively, the AP 102 determines the one ormore DL quality indicators and/or transmit beamforming matrices for aparticular STA 104 based on data included in the feedback frame 1006received from the particular STA 104, such as based on DL channel stateinformation included in the feedback frame 1006 received from theparticular STA 104.

On the other hand, the AP 102 obtains, based on training signals andadditional training signals included in each of the feedback frames1006, UL channel state information (e.g., gain, phase, SNR, etc.)corresponding to the entire bandwidth of the communication channel fromeach of the STAs 104 to the AP 102. Additionally or alternatively, theAP 102 determines UL quality indicators (e.g., SNR, SNIR, signalstrength, etc.) corresponding to each of one or more subbands of thecommunication channel from each of the STAs 104 to the AP 102. The AP102 further identifies one or more candidate subbands for each of theSTAs 104 to be used for UL transmission.

According to the sixth embodiment of the present disclosure, based onthe UL channel state information corresponding to the entire bandwidthof the communication channel from each of the STAs 104 to the AP 102and/or UL quality indicators corresponding to the one or more candidatesubbands of the communication channel from each of the STAs 104 to theAP 102, the AP 102 identifies intended usage of transmission scheme forthe entire bandwidth and/or each of the one or more candidate subbandsfor each of the STAs 104. For example, the AP 102 determines whether theentire bandwidth or each of the one or more candidate subbands for eachof the STA 104 should be used for UL SU-MIMO transmission, UL MU-MIMOtransmission or both.

According to the sixth embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused only for UL SU-MIMO transmission by a STA, the AP 102 develops theUL transmit beamforming matrices for the STA specific to UL SU-MIMOtransmission over the entire bandwidth or the candidate subband in asimilar manner to the first embodiment.

According to the sixth embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused only for UL MU-MIMO transmission by a group of STAs, the AP 102develops the UL transmit beamforming matrices for each STA in the groupspecific to UL MU-MIMO transmission over the entire bandwidth or thecandidate subband in a similar manner to the first embodiment.

According to the sixth embodiment of the present disclosure, if the AP102 determines the entire bandwidth or a candidate subband should beused for UL SU-MIMO transmission by a STA or UL MU-MIMO transmission bya group of STAs, the AP 102 develops both the UL transmit beamformingmatrices for the STA specific to UL SU-MIMO transmission and the ULtransmit beamforming matrices for each STA in the group specific to ULMU-MIMO transmission over the entire bandwidth or the candidate subband.

During a time interval 1028, the AP 102 selects STAs for inclusion intoa DL group for DL MU transmission based on the DL channel stateinformation corresponding to the entire bandwidth and/or DL qualityindicators corresponding to the one or more subbands of thecommunication channel obtained for at least some of the STAs 104 duringthe explicit DL sounding. The AP 102 shall also designate respectivetransmission schemes and allocate respective transmission resources(e.g., subbands in terms of DL OFDMA) to the STAs 104 including the STAsin the DL group. On the other hand, based on the UL channel stateinformation corresponding to the entire bandwidth and/or UL qualityindicators corresponding to the one or more subbands of the ULcommunication channel obtained for at least some of the STAs 104 duringthe explicit UL sounding, the AP 102 selects STAs for inclusion into anUL group for UL MU transmission. The AP 102 shall also designaterespective transmission schemes and allocate respective transmissionresources (e.g., subbands in terms of UL OFDMA) to the STAs in the ULgroup.

During a time interval 1030, the AP 102 transmits respective feedbackframes 1010 to the STAs 104 simultaneously in respective transmissionresources via a DL MU PPDU using respective transmit beamformingmatrices which can be generated from the feedback frames 1006 accordingto the respective designated transmission schemes. For example, if thedesignated transmission scheme for a STA is DL SU-MIMO, then thetransmit beamforming matrices specific to DL SU-MIMO transmission overthe allocated subband for the STA are generated directly or indirectlyfrom the corresponding data of the feedback frames 1006. The DL MU PPDUincludes information on the designated transmission scheme and/or theallocated transmission resource for each of the STAs 104 in the PHYpreamble (e.g., HE-SIG-B field). The AP 102 also transmits respectivedata 1012 to the STAs 104 in the DL group (e.g., STAs 104-1 and 104-3 inthis example) and transmits respective trigger frames 1014 to the STAsin the UL group (e.g., STAs 104-1 and 104-2 in this example) in the sameDL MU PPDU. In this example, the AP 102 transmits an aggregation of thefeedback frame 1010-1, the data 1012-1 and the trigger frame 1014-1, anaggregation of the feedback frame 1010-2 and the trigger frame 1014-2and an aggregation of the feedback frame 1010-3 and the data 1012-3 tothe STAs 104-1, 104-2 and 104-3, respectively, in a DL MU PPDU. The STAs104 obtain respective transmit beamforming matrices for UL MUtransmission directly from the data of the received respective feedbackframes 1010.

According to the sixth embodiment of the present disclosure, thefeedback frame 1010 for a particular STA includes one or more of (i)indications of one or more candidate subbands for the particular STA;(ii) intended usage of transmission scheme corresponding to each of theone or more candidate subbands for the particular STA; (iii) one or morequality indicators corresponding to each of the one or more candidatesubbands for the particular STA; (iv) beamforming feedback correspondingto each of the one or more candidate subbands for the particular STA;(v) intended usage of transmission scheme corresponding to the entirebandwidth for the particular STA; vi) one or more quality indicatorscorresponding to the entire bandwidth for the particular STA; (vii)beamforming feedback corresponding to the entire bandwidth for theparticular STA; and (viii) power control information (e.g. requiredpower adjustment amount), etc.

According to the sixth embodiment of the present disclosure, what isincluded in the beamforming feedback corresponding to the entirebandwidth or a candidate subband for a particular STA depends on theintended usage of transmission scheme for the entire bandwidth or thecandidate subband for the particular STA. If the entire bandwidth or acandidate subband intends to be used only for UL SU-MIMO transmission,the beamforming feedback corresponding to the entire bandwidth or thecandidate subband shall represent the transmit beamforming matricesspecific to UL SU-MIMO transmission. If the entire bandwidth or acandidate subband intends to be used only for UL MU-MIMO transmission,the beamforming feedback corresponding to the entire bandwidth or thecandidate subband shall represent the transmit beamforming matricesspecific to UL MU-MIMO transmission. If the entire bandwidth or acandidate subband intends to be used for UL SU-MIMO or UL MU-MIMOtransmission, the beamforming feedback corresponding to the entirebandwidth or the candidate subband shall represent both the transmitbeamforming matrices specific to UL SU-MIMO transmission and thetransmit beamforming matrices specific to UL MU-MIMO transmission.

According to the sixth embodiment of the present disclosure, each of thetrigger frames 1014 prompts a particular STA in the UL group to transmitdata to the AP 102 at a particular time. Each of the trigger frames 1014also includes information on the designated transmission scheme and/orthe allocated transmission resource for a particular STA in the ULgroup.

During a time interval 1032, if the trigger frames 1014 trigger an ULMU-MIMO transmission, the STAs in the UL group (i.e., STAs 104-1 and104-2 in this example) transmit respective data 1016 simultaneously tothe AP 102 over the entire bandwidth using respective transmitbeamforming matrices specific to UL MU-MIMO transmission over the entirebandwidth. If the trigger frames 1014 trigger an UL OFDMA transmission,the STAs in the UL group transmit respective data 1016 simultaneously tothe AP 102 over respective allocated subbands using respective transmitbeamforming matrices which can be generated directly from the respectivefeedback frames 1010 according to the respective designated transmissionschemes and the respective allocated subbands. For example, if thedesignated transmission scheme for the STA 104-1 is UL SU-MIMO, thetransmit beamforming matrices specific to UL SU-MIMO transmission overthe allocated subband for the STA 104-1 are generated directly from thecorresponding data of the feedback frame 1010-1.

According to the sixth embodiment of the present disclosure, thesounding procedure 1000 begins with explicit DL sounding, followed byexplicit UL sounding. The feedback frames 1006 transmitted by the STAs104 to the AP 102 during explicit DL sounding also function as thesounding frames for explicit UL sounding. Since no dedicated soundingframes are required for explicit UL sounding, the sounding procedure1000 as an explicit bidirectional sounding has a better channelefficiency than a sounding procedure where explicit DL sounding andexplicit UL sounding are performed separately.

According to the present disclosure, the WLAN 100 may support multiplesounding procedures in order to increase system flexibility. Forexample, the WLAN 100 may support three types of sounding procedures: DLsounding procedure, UL sounding procedure and bidirectional soundingprocedure. As a result, the sounding announcement frame sent by the AP102 to the STAs 104 starting a sounding procedure may includeinformation to indicate the type of the sounding procedure. In theexample of FIG. 4, FIG. 6, FIG. 7, FIG. 8 or FIG. 9, the soundingannouncement frame 402, 602, 702, 802 or 902 may include information toindicate the sounding procedure 400, 600, 700, 800 or 900 is an ULsounding procedure. In the example of FIG. 10, the sounding announcementframe 1002 may include information to indicate the sounding procedure1000 is a bidirectional sounding procedure.

<Radio Communication Method >

FIG. 11 is a flow chart illustrating a first example method 1100,implemented by a first communication device, for performing soundingwith a plurality of second communication devices for UL MU transmission,according to the present disclosure. Merely for explanatory purposes,the method 1100 is discussed with reference to FIG. 4, FIG. 6, FIG. 7,FIG. 8 and FIG. 9, and is described in the context of the firstcommunication device as an AP and the second communication devices asSTAs. However, the first communication device may be a suitablecommunication device other than an AP, such as a node in a peer-to-peernetwork while the second communication devices may be suitablecommunication devices other than STAs, such as the nodes in apeer-to-peer network.

At step 1102, the AP obtains, for each STA of the plurality of STAs,channel state information and one or more quality indicatorscorresponding to the entire bandwidth and/or each of one or moresubbands of an OFDM communication channel associated with the STA. Step1102 includes transmitting one or more sounding announcement frames tothe plurality of STAs; receiving a sounding frame from each STA of theplurality of STAs; and obtaining the channel state information and theone or more quality indicators corresponding to the entire bandwidthand/or each of the one or more subbands for each STA of the plurality ofSTAs based on the sounding frame received from the STA. In the exampleof FIG. 4 or FIG. 6, the AP 102 transmits respective soundingannouncement frames 402 or 602 to request the STAs 104-1, 104-2 and104-3, respectively, to transmit respective sounding frames 404 or 604.In the example of FIG. 7, FIG. 8 or FIG. 9, the AP 102 transmits asingle sounding announcement frame 702, 802 or 902 to request the STAs104-1, 104-2 and 104-3 to transmit respective sounding frames 704, 804or 904.

At step 1104, the AP identifies, based on the quality indicatorsobtained for each STA of the plurality of STAs, one or more candidatesubbands for the STA.

At step 1106, the AP develops, based on the channel state informationand the quality indicators obtained for the plurality of STAs, thetransmit beamforming matrices corresponding to the entire bandwidthand/or each of the one or more candidate subbands for each STA of theplurality of STAs. Step 1106 includes identifying, based on the qualityindicators obtained for the plurality of STAs, transmission scheme forthe entire bandwidth and/or each of the one or more candidate subbandsfor each STA of the plurality of STAs; and developing, based on thechannel state information and quality indicators obtained for theplurality of STAs, the transmit beamforming matrices for the entirebandwidth and/or each of the one or more candidate subbands depending onrespective intended usage of transmission scheme for each STA of theplurality of STAs. Step 1106 may also include calculating the requiredpower adjustment amount for each STA of the plurality of STAs.

According to the method 1100, if a candidate subband or the entirebandwidth intends to be used only for UL SU-MIMO transmission, thetransmit beamforming matrices specific to SU-MIMO transmission aredeveloped for the candidate subband or the entire bandwidth. If acandidate subband or the entire bandwidth intends to be used only for ULMU-MIMO transmission, the transmit beamforming matrices specific toMU-MIMO transmission are developed for the candidate subband or theentire bandwidth. If a candidate subband or the entire bandwidth intendsto be used for UL SU-MIMO or MU-MIMO transmission, both the transmitbeamforming matrices specific to SU-MIMO transmission and the transmitbeamforming matrices specific to MU-MIMO transmission are developed forthe candidate subband or the entire bandwidth.

At step 1108, the AP selects, based on the quality indicators obtainedfor at least some of the plurality of STAs, a group of STAs forinclusion into an UL group for UL MU communications, and transmitsrespective feedback information to the plurality of STAs and respectivetrigger information to the STAs in the UL group, wherein the groupincludes two or more STAs of the plurality of STAs. In the example ofFIG. 4, FIG. 6, FIG. 7, FIG. 8 or FIG. 9, the AP 102 selects the STAs104-1 and 104-2 for inclusion into the UL group. The feedbackinformation is described above with reference to FIG. 5. The triggerinformation for a STA in the UL group prompts the STA to simultaneouslytransmit to the AP with other STAs in the UL group at a particular time.The trigger information for a STA in the UL group includes informationon the designated transmission scheme and/or the allocated transmissionresource.

According to the method 1100, in one embodiment, the feedbackinformation for each STA is included in a feedback frame addressed tothe STA and the trigger information for each STA in the UL group isincluded in the feedback frame addressed to the STA. The feedback framesare transmitted by the AP to the plurality of the STAs simultaneouslyvia a DL MU PPDU. In the example of FIG. 9, the AP 102 transmits thefeedback frame 906-1 including feedback information and triggerinformation for the STA 104-1, the feedback frame 906-2 includingfeedback information and trigger information for the STA 104-2 and thefeedback frame 906-3 including feedback information and triggerinformation for the STA 104-3 simultaneously.

According to the method 1100, in one embodiment, the feedbackinformation for each STA is included in a feedback frame addressed tothe STA and the trigger information for the STAs in the UL group isincluded in a trigger frame. The feedback frames are transmitted by theAP to the plurality of STAs simultaneously via a DL MU PPDU prior totransmission of the trigger frame to the STAs in the UL group. In theexample of FIG. 4, the AP 102 transmits the feedback frames 406sequentially to the STAs 104. In the example of FIG. 6 or FIG. 7, the AP102 transmits the feedback frames 606 or 706 simultaneously to the STAs104. After that, the AP 102 transmits the trigger frames 408, 608 or 708to the STAs in the UL group.

According to the method 1100, in one embodiment, the feedbackinformation for each STA is included in a feedback frame addressed tothe STA and the trigger information for each STA in the UL group isincluded in a trigger frame addressed to the STA. An aggregation of thefeedback frame and the trigger frame addressed to each STA in the ULgroup and the feedback frame addressed to each of the plurality of STAswhich is not in the UL group are transmitted to the plurality of STAssimultaneously via a DL MU PPDU. In the example of FIG. 8, the AP 102transmits an aggregation of the feedback frame 806-1 and the triggerframe 808-1 to the STA 104-1, an aggregation of the feedback frame 806-2and the trigger frame 808-2 to the STA 104-2 and the feedback frame806-3 to the STAs 104-3 simultaneously.

At step 1110, the AP receives simultaneous transmission from the STAs inthe UL group in response to the trigger information transmitted at step1108. The simultaneous transmissions received at step 1110 weretransmitted by the STAs in the UL group using the transmit beamformingmatrices generated directly from the data included in the feedbackinformation transmitted by the AP to the STAs in the UL group at step1108. FIG. 12 is a flow chart illustrating a first example method 1200,implemented by one of a plurality of second communication devices, forperforming sounding with a first communication device for UL MUtransmission, according to the present disclosure. Merely forexplanatory purposes, the method 1200 is discussed with reference toFIG. 4, FIG. 6, FIG. 7, FIG. 8 and FIG. 9, and is described in thecontext of the first communication device as an AP and the secondcommunication devices as STAs. However, the first communication devicemay be a suitable communication device other than an AP, such as a nodein a peer-to-peer network while the second communication devices may besuitable communication devices other than STAs, such as the nodes in apeer-to-peer network.

At step 1202, the STA transmits a sounding frame to the AP. Step 1202include receiving a sounding announcement frame from the AP; andtransmitting, in response to the received sounding announcement frame,the sounding frame to the AP. For example, in the example of FIG. 4,FIG. 6, FIG. 7, FIG. 8 or FIG. 9, the STA 104-1 transmits the soundingframe 404-1, 604-1, 704-1, 804-1 or 904-1 to the AP 102 in response toreceiving the sounding announcement frame 402-1, 602-1, 702, 802 or 902.

At step 1204, the STA receives feedback information and triggerinformation from the AP. The feedback information is described abovewith reference to FIG. 5. The trigger information for the STA promptsthe STA to simultaneously transmit to the AP with one or more other STAsat a particular time. The trigger information for the STA also includesinformation on the designated transmission scheme and/or the allocatedtransmission resource.

According to the method 1200, in one embodiment, the feedbackinformation for the STA is included in a feedback frame addressed to theSTA which also includes the trigger information for the STA. The STAreceives the feedback information and the trigger informationsimultaneously. In the example of FIG. 9, the STA 104-1 receives thefeedback frame 906-1 including the feedback information and the triggerinformation.

According to the method 1200, in one embodiment, the feedbackinformation for the STA is included in a feedback frame addressed to theSTA and the trigger information for the STA is included in a triggerframe addressed to the STA. The feedback frame and the trigger frame arereceived by the STA separately. In the example of FIG. 4, FIG. 6 or FIG.7, the feedback frame 406-1, 606-1 or 706-1 is received by the STA 104-1prior to the trigger frame 408, 608 or 708. Alternatively, anaggregation of the feedback frame and the trigger frame is received bythe STA. In the example of FIG. 8, the STA 104-1 receives an aggregationof the feedback frame 806-1 and the trigger frame 808-1.

At step 1206, the STA generates, based on the received feedbackinformation and trigger information, the transmit beamforming matricesfor UL MU transmission. Step 1206 includes identifying, based onreceived trigger information, the designated transmission scheme and theallocated transmission resource; and generating, based on the designatedtransmission scheme and the allocated transmission resource, thetransmit beamforming matrices for UL MU transmission directly from thecorresponding data of the received feedback information.

According to the method 1200, if the received trigger informationindicates UL MU-MIMO transmission over the entire bandwidth, thetransmit beamforming matrices specific to UL MU-MIMO transmission overthe entire bandwidth is generated directly from the corresponding dataof the received feedback information. If the received triggerinformation indicates UL MU-MIMO transmission over the allocatedsubband, the transmit beamforming matrices specific to UL MU-MIMOtransmission over the allocated subband is generated directly from thecorresponding data of the received feedback information. If the receivedtrigger information indicates UL SU-MIMO transmission over the allocatedsubband, the transmit beamforming matrices specific to UL SU-MIMOtransmission over the allocated subband is generated directly from thecorresponding data of the received feedback information.

At step 1208, the STA transmits, in responsive to the triggerinformation, data in the allocated transmission resource according tothe AP simultaneously with the one or more other STAs using the transmitbeamforming matrices generated at step 1206.

FIG. 13 is a flow chart illustrating a second example method 1300,implemented by a first communication device, for performing soundingwith a plurality of second communication devices for cascaded DL and ULMU transmission, according to the present disclosure. Merely forexplanatory purposes, the method 1300 is discussed with reference toFIG. 10, and is described in the context of the first communicationdevice as an AP and the second communication devices as STAs. However,the first communication device may be a suitable communication deviceother than an AP, such as a node in a peer-to-peer network while thesecond communication devices may be suitable communication devices otherthan STAs, such as the nodes in a peer-to-peer network.

At step 1302, the AP transmit a sounding frame as a part of explicit DLsounding to a plurality of STAs after transmitting a soundingannouncement frame to them. In the example of FIG. 10, the AP 102transmits a sounding announcement frame 1002 to the STAs 104-1, 104-2and 104-3, followed by a sounding frame 1004.

At step 1304, the AP receives respective feedback frames for explicit DLsounding from the STAs that function also as respective sounding framesfor explicit UL sounding. In the example of FIG. 10, the AP 102 receivesthe respective feedback frames 1006 from the STAs 104-1, 104-2 and104-3. From the data of the feedback frames, the AP obtains the DLchannel state information and the one or more DL quality indicatorscorresponding to the entire bandwidth and/or each of the one or morepreferred subbands for each STA of the plurality of STAs.

At step 1306, as a part of explicit UL sounding, the AP obtains the ULchannel state information and the one or more UL quality indicatorscorresponding to the entire bandwidth and/or each of the one or moresubbands for each STA of the plurality of STAs based on training signalsand additional training signals included in the feedback frame receivedfrom the STA.

At step 1308, the AP identifies, based on the UL quality indicatorsobtained for each STA of the plurality of STAs, one or more candidatesubbands for the STA.

At step 1310, the AP develops, based on the UL channel state informationand the UL quality indicators obtained for the plurality of STAs, thetransmit beamforming matrices for the entire bandwidth and/or each ofthe one or more candidate subbands for each STA of the plurality ofSTAs. Step 1310 includes identifying, based on the UL quality indicatorsobtained for the plurality of STAs, intended usage of transmissionscheme for the entire bandwidth and/or each of the one or more candidatesubbands for each STA of the plurality of STAs; and developing, based onthe UL channel state information and UL quality indicators obtained forthe plurality of STAs, the transmit beamforming matrices for the entirebandwidth and/or each of the one or more candidate subbands depending onrespective intended usage of transmission scheme for each STA of theplurality of STAs. Step 1310 may also include calculating the requiredpower adjustment amount for each STA of the plurality of STAs.

According to the method 1300, if a candidate subband or the entirebandwidth intends to be used only for UL SU-MIMO transmission, thetransmit beamforming matrices specific to SU-MIMO transmission aredeveloped for the candidate subband or the entire bandwidth. If acandidate subband or the entire bandwidth intends to be used only for ULMU-MIMO transmission, the transmit beamforming matrices specific toMU-MIMO transmission are developed for the candidate subband or theentire bandwidth. If a candidate subband or the entire bandwidth intendsto be used for UL SU-MIMO or MU-MIMO transmission, both the transmitbeamforming matrices specific to SU-MIMO transmission and the transmitbeamforming matrices specific to MU-MIMO transmission are developed forthe candidate subband or the entire bandwidth.

At step 1312, the AP selects, based on the UL quality indicatorsobtained for at least some of the plurality of STAs, a group of STAs forinclusion into an UL group for UL MU transmission. The AP also selects,based on the DL quality indicators obtained for at least some of theplurality of STAs, a group of STAs for inclusion into a DL group for DLMU transmission. The DL or UL group includes two or more STAs of theplurality of STAs. The AP transmits respective feedback information tothe plurality of STAs, the respective DL data to the STAs in the DLgroup and respective trigger information to the STAs in the UL group. Inthe example of FIG. 10, the AP 102 selects the STA 104-1 and the STA104-3 for inclusion into the DL group and selects the STA 104-1 and theSTA 104-2 for inclusion into the UL group. The feedback information isdescribed above with reference to FIG. 5. The trigger information for aSTA in the UL group prompts the STA to simultaneously transmit to the APwith other STAs in the UL group at a particular time. The triggerinformation for a STA in the UL group also includes information on thedesignated transmission scheme and/or the allocated transmissionresource.

According to the method 1300, in one embodiment, the feedbackinformation for each STA is included in a feedback frame addressed tothe STA and the trigger information for each STA in the UL group isincluded in a trigger frame addressed to the STA. An aggregation of thefeedback frame, the DL data and the trigger frame addressed to each STAin the DL and UL groups and the feedback frame and the DL data addressedto each STA which is not in the UL group and but in the DL group, thefeedback frame addressed to each STA which is not in the UL or DL groupare transmitted to the plurality of STAs simultaneously via a DL MUPPDU. In the example of FIG. 10, the AP 102 transmits an aggregation ofthe feedback frame 1010-1, the DL data 1012-1 and the trigger frame1014-1 to the STA 104-1, an aggregation of the feedback frame 1010-2 andthe trigger frame 1014-2 to the STA 104-2 and an aggregation of thefeedback frame 1010-3 and the DL data 1012-3 to the STA 104-3,simultaneously.

At step 1314, the AP receives simultaneous transmission from the STAs inthe UL group in response to the trigger information transmitted at step1314. The simultaneous transmissions received at step 1314 weretransmitted by the STAs in the UL group using the transmit beamformingmatrices generated directly from the data included in the feedbackinformation transmitted by the AP to the STAs in the UL group at step1314.

FIG. 14 is a flow chart illustrating a first example method 1400,implemented by one of a plurality of second communication devices, forperforming sounding with a first communication device for UL MUtransmission, according to the present disclosure. Merely forexplanatory purposes, the method 1400 is discussed with reference toFIG. 10, and is described in the context of the first communicationdevice as an AP and the second communication devices as STAs. However,the first communication device may be a suitable communication deviceother than an AP, such as a node in a peer-to-peer network while thesecond communication devices may be suitable communication devices otherthan STAs, such as the nodes in a peer-to-peer network.

At step 1402, the STA receives a sounding frame from the AP for explicitDL sounding after receiving a sounding announcement frame from the APthat starts a sounding procedure. In the example of FIG. 10, the STA104-1 receives the sounding frame 1004 from the AP 102 after receivingthe sounding announcement frame 1002.

At step 1404, the STA transmits a feedback frame for explicit DLsounding to the AP in response to receiving the sounding frame at step1402 that functions also as a sounding frame for explicit UL sounding.For example, in the example of FIG. 10, the STA 104-1 transmits thefeedback frame 1006-1 to the AP 102 that is used for both explicit DLsounding and explicit UL sounding.

At step 1406, the STA receives feedback information for explicit ULsounding and trigger information from the AP. The feedback informationis described above with reference to FIG. 5. The trigger information forthe STA prompts the STA to simultaneously transmit to the AP with one ormore other STAs at a particular time. The trigger information for theSTA also includes information on the designated transmission schemeand/or the allocated transmission resource.

According to the method 1400, in one embodiment, the feedbackinformation for the STA is included in a feedback frame addressed to theSTA and the trigger information for the STA is included in a triggerframe addressed to the STA. An aggregation of the feedback frame, thetrigger frame and/or the DL data is received by the STA. In the exampleof FIG. 10, the STA 104-1 receives an aggregation of the feedback frame1010-1, the DL data 1012-1 and the trigger frame 1014-1.

At step 1408, the STA generates, based on the received feedbackinformation and trigger information, the transmit beamforming matricesfor UL MU transmission. Step 1408 includes identifying, based onreceived trigger information, the designated transmission scheme and theallocated transmission resource; and generating, based on the designatedtransmission scheme and the allocated transmission resource, thetransmit beamforming matrices for UL MU transmission directly from thecorresponding data of the received feedback information.

According to the method 1400, if the received trigger informationindicates UL MU-MIMO transmission over the entire bandwidth, thetransmit beamforming matrices specific to UL MU-MIMO transmission overthe entire bandwidth is generated directly from the corresponding dataof the received feedback information. If the received triggerinformation indicates UL MU-MIMO transmission over the allocatedsubband, the transmit beamforming matrices specific to UL MU-MIMOtransmission over the allocated subband is generated directly from thecorresponding data of the received feedback information. If the receivedtrigger information indicates UL SU-MIMO transmission over the allocatedsubband, the transmit beamforming matrices specific to UL SU-MIMOtransmission over the allocated subband is generated directly from thecorresponding data of the received feedback information.

At step 1410, the STA transmits, in responsive to the triggerinformation, UL data in the allocated transmission resource according tothe AP simultaneously with the one or more other STAs using the transmitbeamforming matrices generated at step 1408.

<Configuration of an Access Point>

FIG. 15 is a block diagram illustrating example configuration of AP 102according to the present disclosure. The AP 102 includes a hostprocessor 1502 coupled to a network interface 1504. The networkinterface 1504 includes a MAC (Medium Access Control) processor 1506 anda PHY processor 1508. The PHY processor 1508 is coupled to multipleantennas 1510. The network interface 1504 (e.g., the MAC processor 1506and/or the PHY processor 1508) is configured to perform soundingprocedures with the STAs 104 and communicate data with the STAs 104according to the abovementioned embodiments.

<Configuration of a STA>

FIG. 16 is a block diagram illustrating example configuration of STA 104according to the present disclosure. The STA 104 includes a hostprocessor 1602 coupled to a network interface 1604. The networkinterface 1604 includes a MAC processor 1606 and a PHY processor 1608.The PHY processor 1608 is coupled to one or more antennas 1610. Thenetwork interface 1604 (e.g., the MAC processor 1606 and/or the PHYprocessor 1608) is configured to perform sounding procedures with the AP102 and communicate data with the AP 102 according to the abovementionedembodiments.

This disclosure can be applied to a method for performing sounding forUL MU transmission in a wireless communications system.

What is claimed is:
 1. A communication method, comprising: transmitting a sounding frame comprising a training signal; and receiving a first feedback frame from a communication partner device, the first feedback frame comprising first beamforming feedback information, wherein the first feedback frame is transmitted together with at least one second feedback frame by multiuser transmission.
 2. The communication method according to claim 1, wherein one of the at least one second feedback frame comprises second beamforming feedback information, and the multiuser transmission is performed over a plurality of communication links, and the first beamforming feedback information comprises information on one communication link of the plurality of communication links, and the second beamforming feedback information comprises information on another communication link of the plurality of communication links.
 3. The communication method according to claim 1, wherein the first feedback frame and the at least one second feedback frame, transmitted by multiuser transmission, comprise first power control information.
 4. The communication method according to claim 1, comprising: transmitting a frame comprising second power control information before receiving the first feedback frame.
 5. The communication method according to claim 1, wherein the first beamforming feedback information corresponds to an entire bandwidth or one or more subbands of an OFDM communication link, and the first feedback frame comprises a subband indication information.
 6. The communication method according to claim 1, wherein the first beamforming feedback information comprises one or more beamforming matrices.
 7. The communication method according to claim 1, wherein the first feedback frame comprises one or more quality indicators representing SNR.
 8. The communication method according to claim 1, wherein the first beamforming feedback information comprises a compressed beamforming feedback.
 9. The communication method according to claim 1, wherein the first beamforming feedback information is determined based on the training signal.
 10. A communication apparatus, comprising; a communication device which, in operation, transmits a sounding frame comprising a training signal and receives a first feedback frame from a communication partner device, the first feedback frame comprising first beamforming feedback information, wherein the first feedback frame is transmitted together with at least one second feedback frame by multiuser transmission.
 11. The communication apparatus according to claim 10, wherein one of the at least one second feedback frame comprises second beamforming feedback information, and the multiuser transmission is performed over a plurality of communication links, and the first beamforming feedback information comprises information on one communication link of the plurality of communication links, and the second beamforming feedback information comprises information on another communication link of the plurality of communication links.
 12. The communication apparatus according to claim 10, wherein the first feedback frame and the at least one second feedback frame, transmitted by multiuser transmission, comprise first power control information.
 13. The communication apparatus according to claim 10, comprising: the communication device which, in operation, transmits a frame comprising second power control information before receiving the first feedback frame.
 14. The communication apparatus according to claim 10, wherein the first beamforming feedback information corresponds to an entire bandwidth or one or more subbands of an OFDM communication link, and the first feedback frame comprises a subband indication information.
 15. The communication apparatus according to claim 10, wherein the first beamforming feedback information comprises one or more beamforming matrices.
 16. The communication apparatus according to claim 10, wherein the first feedback frame comprises one or more quality indicators representing SNR.
 17. The communication apparatus according to claim 10, wherein the first beamforming feedback information comprises a compressed beamforming feedback.
 18. The communication apparatus according to claim 10, wherein the first beamforming feedback information is determined based on the training signal.
 19. An integrated circuit comprising: control circuitry which, in operation, controls: transmitting a sounding frame comprising a training signal; receiving a first feedback frame from a communication partner device, the first feedback frame comprising first beamforming feedback information, wherein the first feedback frame is transmitted together with at least one second feedback frame by multiuser transmission; and at least one output coupled to the control circuitry which, in operation, outputs a signal. 